1. Field of the Invention
The present invention relates to a semiconductor substrate-supporting apparatus which supports and heats semiconductor substrates inside a vacuum-pumped reaction chamber, and particularly relates to a semiconductor substrate-supporting apparatus which is characterized by the shape of the surface supporting the semiconductor substrate.
2. Description of the Related Art
Conventionally, using CVD equipment, silicon oxide, silicon nitride, insulation films such as polymers containing amorphous carbon or benzene nucleus, conductor films such as tungsten silicide, titanium nitride or aluminum alloy and highly-dielectric films including PZT(PbZr1xe2x88x92xTixO3) or BST(BaxSr1xe2x88x92xTiO3) have been formed on silicon substrates or glass substrates.
To form these films, the low-pressure thermal CVD method and the plasma CVD method are generally used. In the low-pressure thermal CVD method, however, there is a problem that the electrical property of a semiconductor element changes by heat load and does not function as designed, because the semiconductor substrate is exposed to a high temperature above 700xc2x0 C. As semiconductor apparatuses become more highly integrated in recent years, this heat load problem becomes increasingly serious. For this reason, the plasma CVD method, which reduces heat load to the substrate by processing the substrate at a low temperature, has become the mainstream method.
Generally in plasma CVD equipment, a substrate is heated and held at approximately 250xc2x0 C. to 600xc2x0 C. by a ceramic heater heated at 300xc2x0 C. to 650xc2x0 C. The ceramic heater also functions as a susceptor which directly supports the substrate. The ceramic heater is made by burying a resistance heating element and a radio-frequency electrode in the base substance comprising aluminum nitride (AlN). The radio-frequency electrode is embedded at a position which is approximately hundreds to thousands of xcexcm deep from the heater top surface, which directly contacts the semiconductor substrate.
Conventionally, the following have been reported regarding the shapes of the surface of a ceramic heater: U.S. Pat. No. 5,231,690, U.S. Pat. No. 5,968,379 and Japanese Patent Laid-open No.2000-114354 disclose a ceramic heater whose surface is smoothly finished so that the surface of the ceramic heater and the back surface of the substrate perfectly contact. According to this, heat is efficiently conducted from the ceramic heater to the substrate. U.S. Pat. No. 5,306,895, Japan Patent No.2049039 and Japanese Patent Laid-open No.1995-238380 disclose a ceramic heater on whose surface a concave portion with a bore size smaller than the diameter of the substrate is formed and which contacts the back surface of the substrate only at the peripheral portion of the back surface of the substrate. According to this, because thermal conduction from the ceramic heater to the substrate is achieved only at the peripheral portion of the substrate, lowering the temperature at the peripheral portion of the substrate is prevented.
In the case of a ceramic heater whose surface is smoothly finished, because heat rapidly flows into the back surface of a substrate from the ceramic heater immediately after the substrate is placed onto the ceramic heater surface, only the back surface of the substrate expands, causing the substrate to warp. Due to this warping, thermal conduction from the ceramic heater rapidly decreases. It requires several minutes until the warping subsides and the substrate becomes flat. Additionally, it requires more time for the substrate to reach a desired temperature. As a result, it takes time until deposition starts after the substrate is placed onto the ceramic heater, and in the case of single-wafer-processing type semiconductor-manufacturing equipment, productivity is remarkably lowered. If the time for heating the substrate is shortened, because a film is formed in the state where the substrate has not reached the stated temperature, the film with the properties as designed is not obtained. If plasma is discharged while the substrate is warped and deposition is performed, plasma energy converges only on the peripheral portion of the substrate, which projects in the discharge space, and the film thickness becomes uneven across the entire substrate.
In the case of a ceramic heater on whose surface a concave portion with a bore size smaller than the diameter of the substrate is formed, because a rate of heat flowing in the substrate can be reduced due to thermal conduction to the substrate taking place only from the back surface of the peripheral portion of the substrate, warping of the substrate is prevented. If the bore of a concave potion is small, however, an area in which the ceramic heater surface and the back surface of the substrate contact becomes large and the contacting portion is rapidly heated locally and thermally expands. As a result, the entire substrate is deformed and warped. Conversely, if the bore of a concave potion is large and approaches the diameter of the substrate, the back surface of the substrate is not rapidly heated, but there is a risk that the end portion of the substrate may fall into the concave portion of the ceramic heater. If the substrate is placed off-center of the ceramic heater due to a position shift, etc., one end of the substrate falls into the concave portion and the substrate tilts with the opposite end projecting upward. If plasma processing is started in this position, abnormal convergence of the plasma energy (arc) occurs, normal plasma discharge cannot be maintained and a film with uneven thickness and abnormal properties is formed.
Consequently, the object of the present invention is to provide a substrate-supporting apparatus with which no warp or distortion of the substrate occurs and a film with even thickness is formed.
The second object of the present invention is to provide a substrate-supporting apparatus which heats a semiconductor substrate rapidly to a desired temperature and increases the productivity of semiconductor-manufacturing equipment.
The third object of the present invention is to provide a substrate-supporting apparatus which prevents abnormal plasma discharge and which provides stable deposition from a process point of view.
To achieve the above-mentioned objects, the semiconductor-supporting apparatus according to the present invention comprises the following structures in an embodiment:
A semiconductor substrate-supporting apparatus which supports and heats semiconductor substrates inside a vacuum-pumped reaction chamber, wherein on a substrate-supporting surface, a concave portion which comprises a depression slanting from the peripheral portion to the center is provided, the semiconductor substrate is held in a position where the peripheral portion of its back surface contacts the slanting surface of the concave portion, and the concave portion is formed so that an interval between the center of the concave portion and the semiconductor substrate becomes the designated distance.
Preferably, the slanting surface of the concave potion may be a portion of a spherical surface, but can be a conical surface as well.
Specifically, the designated interval between the center of the concave portion and the semiconductor substrate may be 0.05 mm to 0.3 mm.
Preferably, the semiconductor-processing equipment may possess a lip portion which protrudes in a ring-shape at its peripheral surface portion.
For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiments which follow.